A rich web of water criss-crosses the Pearl River Delta, embracing an even denser concentration of industrial zones. Factories great and small are scattered thickly along highways and dirt roads, between cities and country fields. This is China's earliest economic development zone, but it has paid a price: its rivers now are black and lusterless.

Dongbao is one such river. Separating the economic powerhouses of Shenzhen and Dongguan, the river hosts a wealth of industrial zones and building complexes on its banks. In the morning, when the water level is high, the river flows along quietly. In the afternoon, the river is low, exposing discharge pipes of all sizes. The pipe mouths are encrusted with black sediment.

Near the Dongbao River, there's a particularly intriguing "environmental protection company." Shenzhen Resource Environmental Technology ("Shenzhen Resource") claims to specialize in the comprehensive utilization and treatment of industrial waste, with a focus on removing acids and metals. After treatment, the wastewater is piped to somewhere near the Dongbao River.

Shenzhen Resource is not without credentials. It's a subsidiary of Dongjiang Environment, China's first privately operated environmental protection enterprise to be listed abroad (on Hong Kong Stock Exchange's Growth Enterprise Market). Forbes included Dongjiang in its list of Top 100 Potential Enterprises in China consecutively from 2005 to 2007.

Was Shenzhen Resource all it claimed to be? Greenpeace decided to put it to the test.

Flowing past Shenzhen Resources, Dongbao River separates the cities of Shenzhen and Dongguan.

In June of 2009, Greenpeace collected three wastewater samples and two sediment samples outside the factory. In December, the results came back: the supposedly treated water still contained various hazardous chemicals, including acidic wastes, heavy metals, and organic chemical compounds.

More tellingly, certain pollutants were found only at night, including multiple kinds of metals at high concentrations. Among these, manganese, beryllium, copper, and lead were found at concentrations four to 25 times higher than Guangdong province's limit. Manganese and copper exceeded concentration limits by 10 to 74 times. In addition, the discharge was highly acidic, with pH levels far above the allowed standards.

Many of the metals found in the tests are potentially toxic, especially at high concentrations. It's critical to note that large quantities of lead are highly toxic and also accumulate in organisms. Additionally, aquatic animals are very sensitive to dissolved coppers. Worsening the situation is the wastewater's high acidity, which is not only harmful to aquatic life but also increases the water solubility, fluidity and toxicity of metals.

This February, Greenpeace gave the test results to Guangdong province's Environmental Protection Office, requesting them to take action immediately. In June, we finally confirmed through telephone that Shenzhen Resource has been shut down and was in the midst of preparing to move their factory.

Was that the end of the story? Or was it just one fleeting scene in a far larger play that encompasses many more similar tales of environmental pollution?

In reality, it is impossible for end treatment to completely purge wastewater of its hazardous chemicals. At best, treatment plants like Shenzhen Resource can convert hazardous chemicals from one medium to another, such as from wastewater to sediments. What's more their procedures are designed to remove only metals, without testing for other organic pollutants. This is a dangerous neglect, as organic pollutants are more difficult to treat than metals and can also pose significant health threats.

If we really want to end the pollution, then we must go to the source. We need to reduce our use of hazardous chemicals and find less hazardous – or completely non-hazardous – substitutes. We can also push for factories to change their production methods to create fewer toxic by-products. At the very least, factories should immediately cease to discharge wastewater containing hazardous chemicals directly into our rivers. But only if we actively reduce or avoid the use of hazardous chemicals, then can we solve the problem of wastewater pollution at the root.